Taiwanese Patent Publication No. 446070 teaches an upright pump including internal and external cylinders. This conventional pump includes a base, an internal cylinder mounted on the base, a piston movably inserted in the internal cylinder, a rod connected with the piston, an external cylinder mounted on the internal cylinder, a gauge set mounted on the external cylinder and a nozzle in communication with the gauge set through a pipe. The internal cylinder defines a space and an aperture at a lower end in communication with the space. A space is confined between the internal cylinder and the external cylinder. The space is in communication with the space through the aperture. The external cylinder defines an aperture near an upper end. The gauge set is located at the upper end of the external cylinder. A space defined in the gauge set is in communication with the space through the aperture. In pumping, pressurized air flows from the space to the space from which the pressurized air flows to the space defined in the gauge set through the aperture. This conventional pump is complicated in structure and causes trouble for a worker to assemble and therefore entails a high cost for fabrication. The pressurized air travels for a distance twice as much as the length of the internal cylinder, thus reducing efficiency for pumping.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in the prior art.